A Study of Three-Phase Structures in ABC Triblock Copolymers

The microdomain structure of an ABC triblock copolymer consisting of poly(2-hydroxyethyl methacrylate), poly(tert-butyl methacrylate) and poly(2-(perfluorobutyl) ethyl methacrylate) was investigated by means of small-angle X-ray scattering (SAXS) and energy-filtered transmission electron microscopy (EF-TEM) which is based on inelastically scattered electrons by a specific element (F atoms in this case) and known as element spectroscopic imaging (ESI). A three-phase lamellar structure was observed with good contrast for an unstained ultrathin section of the as-cast film of the triblock copolymer by imaging the inelastically scattered electrons at energy-loss of 100 eV. The microdomain structure can be interpreted in accordance with the EF-TEM result. A peculiar SAXS profile where the intensity of the first-order peak was weaker than that of the second-order was observed for the triblock copolymer. Theoretical calculation of the SAXS intensity with a paracrystal model of the four-layer lamellae successfully reproduced the observed SAXS profile.